1. Field of the Invention
The present invention relates to gas turbines, and in particular, the invention relates to use of boiler feedwater for Gas Turbine inlet air temperature control.
2. Description of the Related Art
It is well known in gas turbine operation, that turbine output decreases in proportion to increases in ambient air temperature. However, gas turbine operators frequently encounter peak power generating requirements at elevated ambient temperatures (e.g., due to high air conditioning loads in major cities). It is economical and advantageous to generate additional power through auxiliary systems during those peak power demand periods. One auxiliary system for increasing power input is an inlet misting or fogging system which provides a direct spray of water into the inlet duct which, through an evaporative process, lowers the air temperature to the gas turbine and, hence, increases output.
Compressor inlet misting systems generally attempt to match the spray of water into the inlet duct to the evaporation potential of the air flowing to the gas turbine. Since ambient temperature conditions are variable, a variable spray of water and substantial turndown of the water spray are required. Existing misting systems employ multiple grids each having a substantial number of nozzles to spray the water into the inlet duct. However, as the water supply is turned down, the spray pattern in the inlet duct becomes much less uniform, resulting in less evaporation and more water carryover. Water carryover (i.e., large droplets of water) entering the compressor have potential to erode the initial compressor stage. Additionally, the air flow is disrupted by the nozzles and ancillary piping in the inlet duct, resulting in reduced evaporation. These disruptions often disadvantageously form vortices in the flow downstream of the manifold tubes. Consequently, there has been a need for a misting system which would provide a substantially uniform water spray into the gas turbine compressor at lower than full demand conditions with minimal obstruction to flow and generation of vortices.
One attempt to address this need is disclosed in U.S. Patent Application No. 2005/0102995, entitled “Spray nozzle grid configuration for gas turbine inlet misting system,” published May 19, 2005. This application discloses a mister that includes a plurality of manifolds extending between opposite sides of a duct. Each manifold carries a plurality of nozzles at laterally spaced positions along the length of the manifold. The manifolds are spaced one behind the other in the direction of air flow in the duct and the pipes connecting the nozzles of the intermediate and upstream manifolds bypass the downstream manifolds to provide the nozzles in a common plane perpendicular to the direction of air flow in the duct. This arrangement affords a uniformity of spray and, hence, a uniformity of humidified air to the inlet of the compressor. Although the teachings therein provide many advantages, certain disadvantages of the prior art remain. For example, the use of a separate high-pressure pumping system is costly and in some embodiments, unreliable.
What are needed are methods and apparatus for providing cost efficient and reliable sources of high-pressure water to a gas turbine, such as those disclosed herein.